Iowa caucuses: Newt Gingrich calls Mitt Romney a liar [Video]

As he girds for what is expected to be a disappointing showing in tonight's Iowa caucuses, Republican presidential candidate Newt Gingrich is lashing out, calling rival Mitt Romney a "liar" responsible for negative ads that sunk the former House speaker's campaign.

"This is a man whose staff created the PAC, his millionaire friends fund the PAC, he pretends he has nothing to do with the PAC. It's baloney," Gingrich said on CBS' "The Early Show" (see video below). "He's not telling the American people the truth."

Gingrich is referring to a super-PAC called Restore Our Future, which spent millions of dollars on TV ads in Iowa attacking him just as his campaign surged to the lead there.

The man who began his bid for the White House vowing an upbeat campaign and who later made a virtue of staying positive even as rivals' attacks became sharper has become increasingly downbeat in the final days before the caucuses.

This weekend, he said he felt "Romney-boated," a spin on the "Swift-boating" of John Kerry in the 2004 presidential race.

In the CBS interview, Gingrich said Romney's claim that he was not responsible for the super-PAC ads was "just like his pretense that he's a conservative."

"Here's a Massachusetts moderate who has tax-paying abortions in Romneycare, puts Planned Parenthood in Romneycare, raises hundreds of millions of taxes on businesses, appoints liberal judges to appease Democrats, and wants the rest of us to believe somehow he's magically a conservative," he said.

"I just think he ought to be honest with the American people and try to win as the real Mitt Romney, not try to invent a poll-driven, consultant-guided version that goes around with talking points."

Romney responded in a separate interview on NBC's "Today" show.

"I know the speaker's angry. I don't know why. But my anger's going to be focused on President Obama's failures to put the American people back to work," he said.

Even though Gingrich called Romney a "liar," he still said he'd support him if he were the GOP nominee.

"He would be much less destructive than Barack Obama," Gingrich said.

Gingrich said at an event Monday that he did not think he would win tonight's caucuses, but this morning he changed his tune.

"Everywhere we go, there are a large number of undecided people," he said. "I think anybody could come in first."